In the postwar United States the president's party has always done worse in the midterm congressional elections than in the previous congressional election. Republican administrations exhibit below-average, and Democratic administrations above-average, economic growth in the first half of each term, whereas in the latter halves the two see equal growth. Our rational expectations model is consistent with these two regularities. In presidential elections, voters choose between two polarized candidates. They then use midterm elections to counterbalance the president's policies by strengthening the opposition in Congress. Since presidents of different parties are associated with different policies, our model predicts a (spurious) correlation between the states of the economy and elections. Our predictions contrast with those of retrospective voting models, in which voters reward the incumbent if the economy is doing well before the election. Our model performs empirically at least as well as, and often better than, alternative models.